CODEWITHSUNDEEP
javaandroidcanvas
user3131428
user3131428

Reputation: 27

Drawing shapes one after another on Android's Canvas

Sorry if this question was asked before but I looked around and couldn't really find an answer.

So I'm drawing things onto a SurfaceView using a thread to update any changes made to the screen, and I also have an array of rectangles. How can I draw the rectangles, one after another, and by the end of it, have all of them on the screen? I thought a for loop in the run() method where everything's drawn would've worked, but it just ends up drawing them all at once (which I can understand why). Then, I tried to put a Thread.sleep after every draw in the for loop, but it just waits until after all the rects are drawn before drawing to the canvas. (again, makes sense since the canvas isn't unlocked until after the for loop). If I wanted, say, a two second pause between drawing rects, how could I do that?

Thanks

Edit: Here is the SurfaceView. the pause() and resume() methods are called in the onPause and onResume methods of the activity for which it is the view.

class TestView extends SurfaceView implements Runnable{

SurfaceHolder holder;
Thread t;
Rect[] rectArray;

public TestView(Context context) {
    super(context);
    holder = getHolder();
    rectArray = shapes.getRectArray();
}

@Override
public void run() {
    while(true){
        if(!holder.getSurface().isValid())
            continue;

        Paint p = new Paint();
        p.setColor(Color.BLACK);
        p.setStrokeWidth(10)

        Canvas c = holder.lockCanvas(null);
        c.drawARGB(255, 255, 255, 255);

        for(int i = 0; i<rectArray.length; i++){
            c.drawRect(i,p);
        }

        holder.unlockCanvasAndPost(c);

    }
}

public void pause(){

}

public void resume(){
    t = new Thread(this);
    t.start();
}

}

Upvotes: 0

Views: 697

Answers (1)

ripple182
ripple182

Reputation: 861

I'd probably abstract the thread and SurfaceView and do a basic "game loop" so I have full control over what gets drawn when.

Below is the game loop part:

public class GameLoopThread extends Thread
{
private TestView view;

private boolean running = false;

public GameLoopThread(TestView view)
{
    this.view = view;
}

public void setRunning(boolean run)
{
running = run;
}

@SuppressLint("WrongCall")
@Override
public void run()
{
    long startTime = System.currentTimeMillis();

    while (running)
    {
        Canvas c = null;

        //call update with the number of milliseconds that have passed since the last loop iteration
        view.update(System.currentTimeMillis() - startTime);

        startTime = System.currentTimeMillis();

        try
        {
            c = view.getHolder().lockCanvas();

            synchronized (view.getHolder())
            {
                //call onDraw so my surface draws the rectangles
                view.onDraw(c);
            }
        }
        finally
        {
            if (c != null)
            {
                view.getHolder().unlockCanvasAndPost(c);
            }
        }
    }
}
}

Here is my new surface view:

public class TestView extends SurfaceView
{
     private long totalElapsedTime = 0;
    private Rect[] rectArray;
    private int rectCount = 0;
    private Paint p;
    private GameLoopThread gameLoopThread;

    public TestView(Context context)
    {
        super(context);

       rectArray = shapes.getRectArray();

        p = new Paint();
        p.setColor(Color.BLACK);
        p.setStrokeWidth(10)

       gameLoopThread = new GameLoopThread(this);
       holder = getHolder();
       holder.addCallback(new SurfaceHolder.Callback()
       {

           @Override
            public void surfaceDestroyed(SurfaceHolder holder)
           {
                boolean retry = true;
                gameLoopThread.setRunning(false);
               while (retry)
               {
                  try
                  {
                     gameLoopThread.join();
                     retry = false;
                  }
                  catch (InterruptedException e)
                 {
                 }
              }
          }

          @Override
           public void surfaceCreated(SurfaceHolder holder)
           {
              gameLoopThread.setRunning(true);
              gameLoopThread.start();
           }

           @Override
           public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
           {
           }
    }



    public void update(long elapsedTime)
    {
        totalElapsedTime += elapsedTime;

        //increase the rectCount every second
        rectCount = totalElapsedTime / 1000;

       if(rectCount > rectArray.length)
       {
          rectCount = rectArray.length;
       }
    }


     @Override
     public void onDraw(Canvas canvas)
     {
        canvas.drawARGB(255, 255, 255, 255);

        //draw my rectangles here
        for(int i = 0; i < rectCount; i++)
        {
            canvas.drawRect(i,p);
        }
     }

Upvotes: 1

Related Questions